Diversity transmitter and diversity transmission method

ABSTRACT

The present invention concerns a diversity transmitter and a corresponding diversity transmission method. A symbol matrix is input for being processed, the processing comprising supplying columns of the symbol matrix to a plurality of at least two branches, each branch being supplied to a respective one of spatial channels for transmission. Parallelization is performed so as to provide within each branch at least two parallel channels allocated to a respective user. The symbol matrix signals is subjected on at least one of the branches to an invertible linear transformation with at least one fixed complex weight, the complex weight being different for at least two parallel channels.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to diversity transmitters, and inparticular to diversity transmitters for use in connection with mobilecommunication systems such as UMTS and the like. Also, the presentinvention relates to a corresponding diversity transmission method.

2. Description of the Prior Art

In connection with diversity transmitters, different concepts are beingdiscussed. In general, so called open-loop concepts and closed-loopconcepts can be distinguished, as it is for example outlined in thedocument “A Randomization Technique for Non-Orthogonal Space-Time BlockCodes” by the present inventor and his co-author, presented on IEEEVehicular Technology Conference, May 2001, Rhodes, Greece.

A number of different such open-loop concepts have been proposed in3^(rd) generation partnership project 3 GPP (and/or 3 GPP2). Forexample, in the above mentioned document “A Randomization Technique forNon-Orthogonal Space-Time Block Codes” Applicants have presented the socalled ABBA concept in 3 GPP2. Motorola has proposed a combination ofSTTD+OTD (Space-Time Transmit Diversity+Orthogonal Transmit Diversity),and recently in the TSG-RAN Working Group 1 meeting #15 in Berlin,Germany, Aug. 22–Aug. 25, 2000, Samsung proposed a 2×STTD concept in thesubmitted document “New CPICH Transmission Scheme for 4-antenna transmitdiversity”.

In the document “A Space-Time Coding Concept for a Multi-ElementTransmitter”, by the present inventor and his co-authors, presented inthe Canadian Workshop on Information Theory, June 2001, Vancouver,Canada, Applicants proposed a so-called Trombi-concept which is thesubject of U.S. patent application filed on Mar. 28, 2001. The Trombiconcept (explained later in some greater detail) is considered by theinventor to show currently the best performance. However, up to now theTrombi-concept was mainly implemented in connection with phase-hoppingor phase sweeping arrangements. Phase-hopping and phase sweeping can beused also in the context of the present invention, but with theTrombi-method the transmission methods involving very high data rates inWCDMA downlink can be further enhanced.

Further transmit diversity concepts have been considered in the OFDMliterature (orthogonal frequency division multiplexing). For example,such concepts are discussed in the document “Spatial Transmit diversitytechniques for broadband OFDM systems” by S. Kaiser, published in IEEE,2000, page 1824–1828, (0-7803-6451-1/00).

This proposed concept by Kaiser however requires interleaving overmultiple frequencies for full benefit. A similar approach is discussedin U.S. Pat. No. 6,157,612. Moreover, according to the teaching ofKaiser, a symbol to be transmitted is distributed across severalcarriers, so that for combining the received multipath components, guardintervals are required in order to be able to correctly combine thetransmitted (distributed) symbol parts at the receiving side

Referring back to the above mentioned so-called Trombi concept thefollowing was proposed. A time-varying/hopping phase (for examplepseudo-random) is added to the dedicated channel of a given user at theoutput of STTD encoder (Space-Time Transmit Diversity) (or an encoderbased on some other orthogonal or non-orthogonal concept, see forexample the previous “Randomization technique . . . ” paper).

In one solution with 4 antennas, antennas 2 and 4 are multiplied by acomplex coefficient (constant for two space-time coded [successive]symbols) to result in the following received signal. The received signalr, the symbols S, the transmission channel transfer functions h andcomplex coefficients w are generally given in matrix notationr _(t1) =S ₁(h ₁ +w ₁(t)h ₂)−S ₂*(h ₃ +w ₂(t)h ₄)r _(t2) =S ₂(h ₁ +w ₁(t)h ₂)+S ₁*(h ₃ +w ₂(t)h ₄)  (1)

In a preferred arrangement, it is configured such that w1 (t)=−w2 (t),with constant amplitude=1. Phase changes according to a suitablepseudo-random sequence. For example, it can hop with phases 0, 180, 90,−90, (or with any other sequence) known [a priori] to the terminal(receiver). 8-PSK hopping appears to be sufficient to get achievablegains.

Then, the terminal estimates the channels h1, . . . , h4, for exampleusing common channel pilots (or dedicated pilots) which do not need toapply phase dynamics (for example common channel measurements can bedone as proposed by Samsung in the cited document). Alternatively, theterminal can measure the effective channels h1+w*h2 and h3−w*h4 only.

By knowing the channels and the pseudo-random weights at the transmitterthe intentional phase dynamics can be taken into account and then thedetection reduces to conventional STTD decoding without any complexityincrease.

In essence, the dynamics of the phase-hopping should be a priori fixedor at least it should be known by the UE (for example by suitablesignaling from the transmitter to the receiver). In some cases it mayalso be advantageous if the UE controls the phase-hopping sequence.. Assuch a control procedure is expected to be known to those skilled in theart, these details are supposed to be not needed to be explained here.

With channel coding, providing time diversity, the concept has betterperformance in low Doppler channels than a two antenna STTD concept, asshown in the “Trombi paper”. Phase-hopping diversity can be used also ina way such that the channel estimates are directly taken from aphase-hopping channel. In that case the hopping sequence can have onlyincremental changes, as otherwise the effective channel is changing toorapidly to enable efficient channel estimation. However, in this casethe receiver terminal (User Equipment UE in UMTS) does not necessarilyneed to know that phase-hopping is used at all.

Therefore, in the aforementioned scheme, phase-hopping can weakenchannel estimation performance by the abrupt phase hops, or the hopshave to be quantized to many levels, to thereby approximate aphase-sweep.

The Trombi concept is designed for sequential transmission, and thephase-hopping sequence is defined over multiple time instants, coveringmultiple space-time encoded blocks. In future communication systems thewhole information frame may be transmitted in one or a few symbolintervals (for example if in a CDMA system essentially all downlinkcodes are allocated to one user at a time). In such an extreme case,only one or a few phase-hopping values can be incorporated to thetransmission, and the benefits of the Trombi concept cannot be achieved.

As an example, in “Draft Baseline Text for Physical Layer Portion of the1×EV Specification” 3 GPP2 C.P9091 ver. 0.21, Aug. 24, 2000 (3 GPP2TSG-C working group III) the physical layer of the High Data Rate CDMAsystem is described. This system uses Time Division Multiplexing indownlink and each user can be allocated only one slot, and the pilotsare structured so that only one channel estimate can be obtained forthis one slot.

SUMMARY OF THE INVENTION

The present invention provides an improved diversity transmitter anddiversity transmission method which is free from the above mentioneddrawbacks.

The present invention is a diversity transmitter, comprising: transmitsymbol input means for inputting a symbol matrix to be forwarded to atransmit processing means, the transmit processing means comprisingsupplying means for supplying columns of the symbol matrix to aplurality of at least two branches, each branch being supplied to arespective one of spatial channels for transmission to a receiver, aparallelization means adapted to or which provides within each branch atleast two parallel channels allocated to a respective user, andweighting means adapted to or which subjects the symbol matrix signalson at least one of the branches to an invertible linear transformationwith at least one fixed complex weight, the complex weight beingdifferent for at least two parallel channels.

The present invention is also a diversity transmission method,comprising the steps of inputting a symbol matrix for being processed,the processing comprising supplying columns of the symbol matrix to aplurality of at least two branches, each branch being supplied to arespective one of spatial channels for transmission, performingparallelization so as to provide within each branch at least twoparallel channels allocated to a respective user, and subjecting thesymbol matrix signals on at least one of the branches to an invertiblelinear transformation with at least one fixed complex weight, thecomplex weight being different for at least two parallel channels.

According to further refinements of the present invention (method aswell as transmitter),

-   the invertible linear transformation is a unitary transformation,-   the unitary transformation is represented by a unitary weight matrix    in which at least two elements have different non-zero complex phase    values,-   the parallelization means/step is adapted to or performs multicode    transmission using multiple spreading codes,-   multicode transmission is performed using a Hadamard transformation    by multiplying the symbols with a spreading code matrix H,-   the spreading code matrix is antenna specific,-   the spreading codes are non-orthogonal spreading codes,-   the spreading codes are orthogonal spreading codes,-   the fixed complex weights applied by the weighting means/step are    time-invariant phase shift amounts for the respective parallel    channels,-   the phase shift amounts are independent of the channels in at least    two corresponding parallel channels transmitted out of different    antennas,-   the phase shift amounts are dependent on the channels,-   the weighting matrix is identical for each branch,-   the weighting matrix differs for each branch.-   there is provided a pre-diversification step/means performed    after/arranged downstream inputting and performed before/arranged    upstream processing, the pre-diversification step/means subjecting    the inputted symbol sequence to a diversification, at least one    diversified symbol sequence being subjected to the processing,-   the pre-diversification step/means subjects the input symbol    sequence to at least one of an orthogonal transmit diversity OTD,    orthogonal space-time transmit diversity STTD processing, a    non-orthogonal space-time transmit diversity STTD processing, delay    diversity DD processing, Space-Time Trellis-Code processing, or    Space-Time Turbo-Code processing,-   the input symbol sequence is a channel coded sequence,-   the channel coding is Turbo coding, convolutional coding, block    coding, or Trellis coding,-   the pre-diversification step/means subjects the input symbol to more    than one of the processings, the processings being performed in    concatenation,-   the phase offsets in parallel channels differ by a fixed amount,-   the phase offsets in parallel channels differ by a maximum possible    amount,-   the phase offsets in parallel channels cover a full complex circle    of 360°,-   the phase offsets in parallel channels are taken from a Phase Shift    Keying configuration,-   the used phase offsets are signaled to the receiver,-   the phase offsets are at least partially controlled by the receiver    via a feedback channel,-   all columns of the symbol matrix contain the same symbols,-   the symbol matrix is an orthogonal space-time block code,-   the symbol matrix is a non-orthogonal space-time block code,-   at least one column of the symbol matrix is different from another    column,-   the symbol matrix contains at least two space-time code matrices,    each modulating different symbols,-   all columns of the symbol matrix have different symbols, each    parallel channel transmits from respective spatial channel in    parallel at least two symbols allocated to the spatial channel.

Still further, for example, the spreading codes are scrambeled with atransmission unit specific scrambling sequence (for example same for allantennas in one base station or transmission unit), the weighting meansapplies a complex weighting matrix [having in its diagonal thetime-invariant phase shift amounts] for the respective symbol sequences,said symbol sequences modulating the respective parallel channels.

Also, for example, the pre-diversification means/step subjects the inputsymbol to at least one of an orthogonal transmit diversity OTDprocessing, parallel transmission (in this case pre-diversificationtakes as an input e.g. 4 different symbols, performs serial to parallelconversion and transmits the 2 symbols in parallel simultaneously fromtwo antennas or branches, this increasing the data rate by factor oftwo), orthogonal space-time transmit diversity (STTD, assuming arbitrarynumber of outputs), a non-orthogonal space-time transmit diversity STTDprocessing (maintaining the rate at 1 or increase the rate beyond 1, butallowing some self-interference), delay diversity DD processing,Trellis-Code processing, Convolutional Code Processing or Turbo-Codeprocessing, the pre-diversification means subjects the input symbol tomore than one of the processings, the processings being performed inconcatenation. So, there exists a system in which there is first channelcoding, for example by a Turbo/Convolutional code, the output is givento OTD, S/P, STTD or NO-STTD, and there is typically interleaving afterTurbo coding.

Thus, by virtue of the present invention the above mentioned drawbacksinherent to known prior art arrangements are removed.

In particular, the following advantages can be achieved:

-   improvement of performance with burst transmission,-   no interference with channel estimation,-   simple to implement at the transmitter, as no semi-continuous sweep    is required,-   no interleaving over multiple frequencies is required for full    benefit,-   no guard intervals are required in order to be able to correctly    combine the transmitted (distributed) symbol parts at the receiving    side.

In particular, one embodiment of the present invention achievesobtaining similar effective received channels (eq. 1, defined over time)even without making use of phase-hopping, and even if the transmissioninterval is very short and highly parallel burst transmission is used.In another embodiment the invention achieves randomizing thecorrelations-within a non-orthogonal space-time code even if thetransmission interval is very short.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greaterdetail with reference to the accompanying drawings, in which

FIG. 1 shows a simplified block diagram of a basic configuration of adiversity transmitter according to the present invention and operatingaccording to the basic diversity transmission method according to thepresent invention, and

FIG. 2 shows a modification a simplified block diagram of a modifiedconfiguration of a diversity transmitter according to the presentinvention, including a pre-diversification means.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the diversity transmitter and method according to the presentinvention there are multiple parallel transmissions out of at least twospatial channels (which may be antennas or beams). Namely, basicallythere need to be at least two (logical) parallel channels (for examplespreading codes) allocated to a given user (receiver), the parallelchannels are transmitted out of at least two spatial channels such astransmit antennas (or beams), for example like in Trombi, at least two(preferably 8, according to Trombi results) of the parallel channels,transmitted out of at least one of said spatial channel (antenna) areweighted by multiplication with a fixed complex weight, the complexweight being different for at least two parallel channels.

This is explained in greater detail with reference to FIG. 1.

FIG. 1 shows a diversity transmitter, i.e. a simplified block diagram ofa basic configuration of a diversity transmitter according to thepresent invention. Transmissions out of antennas (representing anexample of spatial channels) A1, . . . , Am are experiencing theinfluence of respective transmission channels a1, . . . , am beforereception at a receiver. In general, a symbol b to be transmitted isprocessed at the transmitter, transmitted via the transmissionchannel(s) and received at the receiver, where it is subjected to areception processing in order to reconstruct the initially transmittedsymbol b. Reception processing involves channel estimation in order tocompensate for the influence of the transmission channels. The symbol bas well as the transmission channels, that is channel impulse response athereof, are in matrix notation.

The diversity transmitter comprises a transmit symbol input means 1 forinputting the symbol b (symbol matrix or a sequence of symbol matrices)to be forwarded to a transmit processing means 2. The transmitprocessing means 2 in turn comprises supplying means 2 a for supplyingthe symbol b to a plurality of at least two branches, each branch beingsupplied to a respective one of transmit antennas A1, . . . , Am (thatis spatial transmit channels) for transmission to a receiver. Aparallelization means 2 b is adapted to or provides within each branchat least two parallel channels allocated to a respective user (i.e.receiver), and a weighting means 2 c is adapted to multiply the symbolsignals on at least one of the branches with a fixed complex weight, thecomplex weight being different for at least two parallel channels.

In FIG. 1, the parallelization is performed in each of the shown twobranches, while the weighting is effected only in the lower branch.Nevertheless, it may be performed in the upper branch instead of thelower branch or in both branches.

The parallelization means 2 b is adapted to or performs a multicodetransmission WCDMA such as for example Hadamard transformation bymultiplying with a user and/or service specific spreading code matrix H,and the spreading code matrix may be antenna specific. In theillustrated example, however, the same spreading code matrix has beenselected for each antenna or spatial channel. If a Hadamardtransformation is applied for spreading, scrambling prior to outputtingthe processed symbols to the antennas is performed, while however, suchscrambling and RF processing is omitted from the illustration forpurposes of keeping the illustration simple.

The received signal r at the receiver after multipath propagation overthe channels a1, a2 (am with m=2) is thenr=a ₁ Hb+a ₂ Hdiag([exp(jφ ₁), . . . , exp(jφ _(n))])b+n  (2)where the diagonal matrix “diag” consists of the fixed complex weightsof a weighting matrix W, and coefficients a1, a2 refer to channelcoefficients (i.e. the respective channel impulse response) between agiven antenna and the terminal. H is the matrix of spreading codes, nrepresents a noise component, and b the vector/matrix of transmittedsymbols

This basic embodiment may be concatenated with pre-diversificationperformed by a pre-diversification means 3 arranged downstream saidinput means 1 and upstream said transmit processing means 2.

FIG. 2 shows an example of such a diversity transmitter, with the inputmeans being omitted from the figure. The pre-diversification means 3,for example performing STTD or another diversity concept, is adapted toor subjects the inputted symbol matrix b to a diversification, eachdiversified symbol (vectors/sequences) b1, b2 being supplied to theprocessing means. As shown in the example in FIG. 2, a first diversifiedsignal b1 is supplied to a processing means 21, while a seconddiversified signal b2 is supplied to a processing means 22. Theprocessing means 21 and 22 are illustrated as being identical to eachother, while this is not required to be. They may differ in terms of thespreading matrix H used, the weighting matrix W used, and even in thenumber m of spatial channels (antennas or beams) used. In a multiuserCDMA system where at least one transmission applies the multicodetransmission, it is preferred that the processing means 21 and 22 arethe same, but that different users select different codes from thespreading matrix. Then the different code-multiplexed users do notinterfere with each other, if the matrix is orthogonal.

When concatenating this with other transmission diversity concepts asshown in FIG. 2, the symbols {b} need to be defined differently. Inparticular, a case is considered in which 4 antennas are used, and inwhich two parallel transmissions (both transmitting from two antennas)are combined with Orthogonal Transmit Diversity (OTD), such that theyhave the same symbol sequences, but different antenna specificorthogonal spreading matrices H1 and H2. Then one receives a signalr=a ₁ H ₁ b+a ₂ H ₁ diag([exp(jφ ₁), . . . , exp(jφ _(n))])b+a ₃ H ₂ b+a₄ H ₂ diag([exp(jφ ₁), . . . , exp(jφ _(n))])b+n  (3)with four subscripts 1, . . . 4 for the channels as in the example thereare m=4 transmission antennas, two subscripts 1, 2, for parallel (multi)codes H1, H2 in different transmission antenna branches (due to OTD). Inthis case they are preferably different submatrices of a Hadamard codematrix, and thereby orthogonal to each other. The letter n againrepresents a noise component.

In alternative embodiments at least partly different symbolssequence/vectors b1 and b2 are transmitted from the two differentantenna pairs. Then, the received signal is given byr=a ₁ H ₁ b ₁ +a ₂ H ₁ diag([exp(jφ ₁), . . . , exp(jφ _(n))])b ₁ +a ₃ H₂ b ₂ +a ₄ H ₂ diag([exp(jφ ₁), . . . , exp(jφ _(n))])b ₂ +n  (3′)

For example, the symbol vectors b1 and b2 may represent two differentinformation substreams (possibly after channel coding), formed withserial to parallel (S/P) conversion. Then, the transmission conceptincreases the data rate by a factor of two. If the spatial channels fromthe transmit antennas to the receive antennas are sufficiently differentH1 can equal H2 and still be able to detect the symbol streams b1 andb2. In alternative embodiments, the symbol streams b1 and b2 may eachbelong to different branches of the STTD (or any other space-time code,including Space-time spreading). As an example, with STTD, the b1=(c1c2) and b2=(−c2*c1*), where c1 and c2 are the (complex) symbolsforwarded to parallel transmission means. In this case these symbolsequences are separable (in fact, orthogonal) due the properties of thespace-time code, and the matrices H1 and H2 are preferably identical.Note that in this case the symbol rate remains at 1 since it takes twotime intervals to transmit two symbols. However, the diversity order isdoubled. The code matrices are preferably orthogonal, for exampleHadamard codes, or rotated (scrambled) Hadamard codes, or nearlyorthogonal, such as well known Gold codes. Any other orthogonalspace-time code can be used.

It is to be noted that the antenna specific parallel channels H, H1 andH2 above can have an arbitrary spreading factor, and can be implementedin code domain (parallel codes), or with orthogonal carriers(frequencies).

This can be combined with any other transmit diversity concept, when forexample extending the number of transmit antennas further. One canconcatenate delay diversity, non-orthogonal space-time codes, orthogonalspace-time codes, space-time trellis codes, Turbo-coded transmitdiversity and various others with the proposed concept. Also, if onedoes not have a sufficient number of parallel channels but a sufficientnumber of successive symbol intervals, one can still use phase hopping,as the prior art proposes.

The complex weights should be defined so that consecutive coded bits orsymbols see a different channel. In one example, the parallel channelsapply phases with 0, 180, 90, −90 degree offsets. Preferably, there areat least eight states (for example from PSK alphabet), such that thephase sequence visits all states once and such that the “path length” ismaximized.

One can apply the fixed phase coefficients also in analogy with the ABBAconcept and/or randomized ABBA concept (RABBA) if there are at leastthree transmit paths, e.g. three different transmit antennas. This isthen effected in the pre-diversification means 3. In this case asequence of symbols is input to the ABBA code (for example as inTrombi), each output of the ABBA code (columns of the ABBA, or someother non-orthogonal space-time code matrix) are directed to differenttransmit antennas, and the sequence in each different branch issubjected to multicode transmission, such that at least in one branch atleast one code is subjected to a fixed phase rotation. Note, that thiscan be implemented also so that selected symbols in a given branch ofthe non-orthogonal code have a rotated signal constellation.

It is assumed that there are four antennas, and that different columnsof the ABBA code are transmitted out of antennas 1, . . . , 4 inparallel with different K spreading (Walsh) codes (w_k) or carriers (forexample vectors from the IFFT matrix in OFDM). In this case thetransmitted signal for a packet of 4*K (number 4 comes from theparticular ABBA construction, where in this example the 2×2 matrices Aand B both contain 2 symbols for example from QPSK alphabet, there isessentially the same symbol construction in STTD, described earlier)symbols are given by equation (4) below

$\begin{matrix}{\sum\limits_{k = {1:K}}^{\;}\begin{bmatrix}{w_{k}A_{k}} & {w_{k}\mspace{14mu}\exp\mspace{11mu}\left( {j\;\theta_{k}} \right)\mspace{11mu} B_{k}} \\{w_{k}B_{k}} & {w_{k}\mspace{11mu}\exp\mspace{11mu}\left( {j\;\theta_{k}} \right)A_{k}}\end{bmatrix}} & (4)\end{matrix}$where matrices A and B are the elements of the so called ABBA matrix(ABBA can be replaced here by any other non-orthogonal block code,optimized for one of multiple receive antennas). Each paralleltransmission, indexed by k, carries different ABBA symbol matrices, andthe signals are transmitted out of antennas.

In the aforementioned example several parallel ABBA transmissions havedifferent complex weights modulating the output of at least one antenna(in the example in previous equation, two antennas).

Thus, there is no time index in the complex phasors (phasors means themultiplication factor achieving the time-invariant phase shift). Notethat the parallel Trombi-concept can be described also with eq. 4, whentwo (and only two) B and A matrices switch place (are exchanged).

In terms of other conceivable embodiments it is clear that a similarapproach can be used for any system with more than two antennas. Also,the number of antennas need not to be an even number as in theillustrated examples in FIGS. 1 and 2, but may be arbitrary.

The parallel weighted channels can be transmitted to non-fixed beamswhich are defined for example by long-term feedback from the receiver orby receive measurements, or by both; or they can be transmitted to fixedbeams.

The complex weights do not need to have unit norm but may have a valuediffering from 1.

The previous phase-hopping concept has been converted according to thepresent invention to a phase-modulation concept which is applicable forexample to the parallel channels in HDR (High Data Rate) or to any highrate transmission concept in which a number of parallel channels areused with at least two transmit antennas.

The invention has the advantage that it avoids the previous time-variantphase-offset arrangements, thereby resulting in a simpler receiverimplementation in the user equipment. The concept can be implemented atbase band using different rotated symbol constellations in parallelchannels prior signal spreading.

The performance of the concept, when combined with STTD is similar aswith Trombi, when this is used in place of phase hopping.

Best symbol error rate is likely to be obtained with ABBA based/typesolution with fixed phase offsets (in the presence of at least 3antennas/channels). In that case one may be able to use a very high ratechannel code, and some ARQ solution for “good enough” performance (withARQ the phase can change if the retransmission occurs well with thechannel coherence time).

With OFDM, the ABBA solution randomizes the interference across multipleantennas, and typically requires that a simple (linear or nonlinear)interference cancellation concept is used in the receiver to mitigate tonon-orthogonality of the space-time code. With parallel-Trombi, it issimpler, as the codes and symbols remain orthogonal. No such CDMA basedsystem (HDR, HSDPA) without the space-time code component even for twotransmit antennas achieving the advantages described herein before ispresently known to the inventors. In any case it is beneficial then touse one of the parallel channels for channel estimation and fix thephase offset for the parallel channels a priori so that the receiver ofthe user equipment need not estimate the channel for each of theparallel channels separately. However, if the parallel channels haveindependent channel estimators, the invention is backward compatible tosuch a system. It is also possible that the transmitter can use theinvention if it so desires and the receiver blindly detects this. Blinddetection can be done for example by demodulating the signal using theproposed concept (fixed phase offset) and without using the proposedconcept, and selecting the one that gives better performance (forexample symbol reliabilities at the output of the decoder).

It is likely that the performance increase will be the highest in indoorchannels (7–9 dB's compared to single antenna transmission).

In particular, it is to be noted that the parallelization means isadapted to achieve a multicode transmission (WCDMA, Wideband CodeDivisional Multiple Access). In this case, the parallelization meansuses a Hadamard transformation (Hadamard matrix) or a submatrix of aHadamard matrix. Also, parallelization is then followed by scramblingprocessing prior to transmission out of the antennas. If no Hadamardmatrix for prallelization is to be used, so-called Gold codes may beused instead, which alleviates the necessity for subsequent scrambling.With scrambling, however, better autocorrelation properties for thesignal can be obtained to make use of RAKE diversity. Alternatively, theparallelization means may be adapted to or which performs an InverseFast Fourier Transformation IFFT (in connection with OFDM).

Furthermore, it is pointed out that the weighting means are adapted toor which performs not only a simple multiplication but a lineartransformation. To this end, the weighting matrix may preferably be amatrix of the kind such that the weighting matrix W is unitary, i.e.that when multiplied with its conjugate complex transposed matrix W^(H)yields the identity matrix I having only values of “1” in its diagonal(W^(H)*W=I).

Moreover, in case the pre-diversification means subject the symbol to anon-orthogonal space-time code, non-orthogonal space-time block codessuch as ABBA, Randomized ABBA (RABBA), or Alamouti Code (STTD in WCDMA)are advantageously to be used.

Also, the sequence of parallelization and weighting may be reversed,provided that the used signal processing is suitably modified. Thesymbols prior parallel transmission can be subjected to weighting or theparallel channels (modulated spreading codes) can the subjected toweighting.

Thus, according to the present invention, the phases in (selectedparallel channels) in m-1 out of m antennas are randomized by fixedcomplex weights so that destructive combination does not dominate. If nparallel channels are present due to parallelization, a n dimensionalweighting matrix can be used, although a two-dimensional matrix could besufficient. In an n dimensional matrix, some of the complex phases maybe set to zero, in which case no weighting is imposed on that particularchannel.

It is to be noted that signals as described in this application arerepresented in matrix notation. Thus, the symbol and/or symbol sequenceis to be understood to be in matrix notation. Those matrices are forexample described in “Complex Space-Time Block Codes For Four TxAntennas”, O. Tirkkonen, A. Hottinen, Globecom 2000, December 2000, SanFrancisco, US for orthogonal space-time codes with a different number oftransmit antennas. (A single symbol would correspond to a sequence of aminimum sequence length, for example length one).

Also, a receiver adapted to which receives the signals transmittedaccording to the present invention will have to be provided inparticular with a corresponding despreading functionality, adapted to orwhich performs the inverse operation as compared to the transmittingside. This inverse operation can be expressed by the subjecting thereceived signal to an inverse processing, represented by multiplyingwith the inverse matrices (H⁻¹, W⁻¹). Apart therefrom, a receivercomprises RF parts, a channel estimator, a symbol detector (for examplebased on maximum likelihood, maximum a posteriori, iterativeinterference cancellation principles), and multiplexer.

Accordingly, as has been described herein above, the present inventionconcerns a diversity transmitter, comprising: transmit symbol inputmeans (1) for inputting a symbol matrix (b) to be forwarded to atransmit processing means (2), the transmit processing means comprisingsupplying means (2 a) for supplying the columns of the symbol matrix toa plurality of at least two branches, each branch being supplied to arespective one of spatial channels (A1, . . . , Am) for transmission toa receiver, a parallelization means (2 b) adapted to or which provideswithin each branch at least two parallel channels allocated to arespective user, and weighting means (2 c) adapted to or which subjectsthe symbol matrix signals on at least one of the branches to aninvertible linear transformation with a fixed complex weight, thecomplex weight being different for at least two parallel channels. Thepresent invention also concerns a corresponding diversity transmissionmethod.

Although the present invention has been described herein above withreference to its preferred embodiments, it should be understood thatnumerous modifications may be made thereto without departing from thespirit and scope of the invention. For example, the transmitter may bethe mobile terminal, and the receiver the base station, or anothermobile terminal. Furthermore, the spatial channel may include so calledpolarization diversity channels. Power control may be applied to theparallel channels separately or jointly. Some of the parallel channelsmay provide a different quality of service (for example BER) and havedifferent channel coding (error correction/error detection), and/ordifferent relative transmit powers. Some of the transmit antennas maybelong to different base stations in which case the invention can beused to provide macrodiversity or soft handoff. It is intended that allsuch modifications fall within the scope of the appended claims.

1. A diversity transmitter, comprising: a transmit symbol input devicefor inputting a symbol matrix to be forwarded to a transmit processingdevice; the transmit processing device comprising a supplying device forsupplying columns of the symbol matrix to a plurality of at least twobranches, each branch being supplied to a respective one of spatialchannels for transmission to a receiver; a parallelization device forproviding within each branch at least two parallel channels allocated toa respective user; and a weighting device for subjecting the symbolmatrix signals on at least one of the branches to an invertible lineartransformation with at least one fixed complex weight, the complexweight being different for at least two parallel channels.
 2. Adiversity transmitter according to claim 1, wherein: the invertiblelinear transformation is a unitary transformation.
 3. A diversitytransmitter according to claim 2, wherein: the unitary transformation isrepresented by a unitary weight matrix in which at least two elementshave different non-zero complex phase values.
 4. A diversity transmitteraccording to claim 1, wherein: the parallelization device performsmulticode transmission using multiple spreading codes.
 5. A diversitytransmitter according to claim 4, wherein: multicode transmission isperformed using a Hadamard transformation by multiplying the symbolswith a spreading code matrix.
 6. A diversity transmitter according toclaim 4, wherein: the spreading code matrix is antenna specific.
 7. Adiversity transmitter according to claim 4, wherein: the spreading codesare non-orthogonal spreading codes.
 8. A diversity transmitter accordingto claim 4, wherein: the spreading codes are orthogonal spreading codes.9. A diversity transmitter according to claim 1, wherein: the fixedcomplex weights applied by the weighting device are time-invariant phaseshift amounts for the respective parallel channels.
 10. A diversitytransmitter according to claim 9, wherein: the phase shift amounts areindependent of the channels in at least two corresponding parallelchannels transmitted out of different antennas.
 11. A diversitytransmitter according to claim 9, wherein: the phase shift amounts aredependent on the channels.
 12. A diversity transmitter according toclaim 9, wherein: the weighting matrix is identical for each branch. 13.A diversity transmitter according to claim 9, wherein: the weightingmatrix differs for each branch.
 14. A diversity transmitter according toclaim 9, wherein: the phase offsets in parallel channels differ by afixed amount.
 15. A diversity transmitter according to claim 9, wherein:the phase offsets in parallel channels differ by a maximum possibleamount.
 16. A diversity transmitter according to claim 9, wherein: thephase offsets in parallel channels cover a full complex circle of 360°.17. A diversity transmitter according to claim 9, wherein: the phaseoffsets in parallel channels are taken from a Phase Shift Keyingconfiguration.
 18. A diversity transmitter according to claim 9,wherein: the used phase offsets are signaled to the receiver.
 19. Adiversity transmitter according to claim 9, wherein: the phase offsetsare at least partially controlled by the receiver via a feedbackchannel.
 20. A diversity transmitter according to claim 1, comprising: apre-diversification device arranged downstream from the input device andupstream the transmit processing device; the pre-diversification devicesubjects the inputted symbol sequence to a diversification, at least onediversified symbol sequence being supplied to the processing device. 21.A diversity transmitter according to claim 20, wherein: thepre-diversification device subjects the input symbol sequence to atleast one of an orthogonal transmit diversity, orthogonal space-timetransmit diversity processing, a non-orthogonal space-time transmitdiversity processing, delay diversity processing, Space-TimeTrellis-Code processing, or Space-Time Turbo-Code processing.
 22. Adiversity transmitter according to claim 21, wherein: thepre-diversification device subjects the input symbol to more than one ofthe processings, the processings being performed in concatenation.
 23. Adiversity transmitter according to claim 1, wherein: the input symbolsequence is a channel coded sequence.
 24. A diversity transmitteraccording to claim 23, wherein: the channel coding is Turbo coding,convolutional coding, block coding, or Trellis coding.
 25. A diversitytransmitter according to claim 1, wherein: all columns of the symbolmatrix contain identical symbols.
 26. A diversity transmitter accordingto claim 1, wherein: the symbol matrix is an orthogonal space-time blockcode.
 27. A diversity transmitter according to claim 1, wherein: thesymbol matrix is a non-orthogonal space-time block code.
 28. A diversitytransmitter according to claim 1, wherein: at least one column of thesymbol matrix is different from another column.
 29. A diversitytransmitter according to claim 1, wherein: the symbol matrix contains atleast two space-time code matrices, each modulating different symbols.30. A diversity transmitter according to claim 1, wherein: all columnsof the symbol matrix have different symbols, each parallel channeltransmits from respective spatial channel in parallel at least twosymbols allocated to the spatial channel.
 31. A diversity transmissionmethod, comprising: inputting a symbol matrix for being processed, theprocessing comprising supplying columns of the symbol matrix to aplurality of at least two branches, each branch being supplied to arespective one of spatial channels for transmission; performingparallelization so as to provide within each branch at least twoparallel channels allocated to a respective user; and subjecting thesymbol matrix signals on at least one of the branches to an invertiblelinear transformation with at least one fixed complex weight, thecomplex weight being different for at least two parallel channels.
 32. Amethod according to claim 31, wherein: the invertible lineartransformation is a unitary transformation.
 33. A method according toclaim 32, wherein: the unitary transformation is represented by aunitary weight matrix in which at least two elements have differentnon-zero complex phase values.
 34. A method according to claim 31,wherein: the parallelization performs multicode transmission usingmultiple spreading codes.
 35. A method according to claim 34, wherein:multicode transmission is performed using a Hadamard transformation bymultiplying the symbols with a spreading code matrix.
 36. A methodaccording to claim 34, wherein: the spreading code matrix is antennaspecific.
 37. A method according to claim 34, wherein: the spreadingcodes are non-orthogonal spreading codes.
 38. A method according toclaim 34, wherein: the spreading codes are orthogonal spreading codes.39. A method according to claim 31, wherein: the fixed complex weightsapplied by a weighting device are time-invariant phase shift amounts forthe respective parallel channels.
 40. A method according to claim 39,wherein: the phase shift amounts are independent of the channels in atleast two corresponding parallel channels transmitted out of differentantennas.
 41. A method according to claim 39, wherein: the phase shiftamounts are dependent on the channels.
 42. A method according to claim39, wherein: the weighting matrix is identical for each branch.
 43. Amethod according to claim 39, wherein: the weighting matrix differs foreach branch.
 44. A method according to claim 39, wherein: the phaseoffsets in parallel channels differ by a fixed amount.
 45. A methodaccording to claim 39, wherein: the phase offsets in parallel channelsdiffer by a maximum possible amount.
 46. A method according to claim 39,wherein: the phase offsets in parallel channels cover a full complexcircle of 360°.
 47. A method according to claim 39, wherein: the phaseoffsets in parallel channels are taken from a Phase Shift Keyingconfiguration.
 48. A method according to claim 39, wherein: the usedphase offsets are signaled to the receiver.
 49. A method according toclaim 39, wherein: the phase offsets are at least partially controlledby the receiver via a feedback channel.
 50. A method according to claim31, comprising: a pre-diversification step pefformed after inputting andbefore processing; the pre-diversification step subjects the inputtedsymbol sequence to a diversification, at least one diversified symbolsequence being subjected to the processing.
 51. A method according toclaim 50, wherein: the pre-diversification step subjects the inputsymbol sequence to at least one of an orthogonal transmit diversity,orthogonal space-time transmit diversity processing, a non-orthogonalspace-time transmit diversity processing, delay diversity processing,Space-Time Trellis-Code processing, or Space-Time Turbo-Code processing.52. A method according to claim 51, wherein: the pre-diversificationstep subjects the input symbol to more than one of the processings, theprocessings being performed in concatenation.
 53. A method according toclaim 31, wherein: the input symbol sequence is a channel codedsequence.
 54. A method according to claim 53, wherein: the channelcoding is Turbo coding, convolutional coding, block coding, or Trelliscoding.
 55. A method according to claim 31, wherein: all columns of thesymbol matrix contain identical symbols.
 56. A method according to claim31, wherein: the symbol matrix is an orthogonal space-time block code.57. A method according to claim 31, wherein: the symbol matrix is anon-orthogonal space-time block code.
 58. A method according to claim31, wherein: at least one column of the symbol matrix is different fromanother column.
 59. A method according to claim 31, wherein: the symbolmatrix contains at least two space-time code matrices, each modulatingdifferent symbols.
 60. A method according to claim 31, wherein: allcolumns of the symbol matrix have different symbols, each parallelchannel transmits from respective spatial channel in parallel at leasttwo symbols allocated to the spatial channel.